Underground drainage facility, vertical-shaft multi-stage adjustable vane pump, and method of running drainage pump

ABSTRACT

A vertical-shaft multi-stage pump has adjustable vanes on its lower stage. A vane angle operating mechanism has an operating shaft extending through a hollow portion of the drive shaft of the upper stage and a link mechanism connected to the operating shaft and the adjustable vane impeller for converting axial motion of the operating shaft into vane angle rotational motion. The pump is particularly suited for use in an underground drainage system.

This is a division of application Ser. No. 988,755 filed Dec. 10, 1992,now U.S. Pat. No. 5,360,290.

BACKGROUND OF THE INVENTION

The present invention relates to an underground drainage facilityarranged such that influent fluids such as rainwater or the like flowinginto water channels including small rivers is collected in an inflowchannel and, more particularly, to a large capacity underground floodwaywith a slightly inclined inflow water channel which is provided in anunderground location, with the floodway having a large depth of between15 to 60 m, wherein the collected influent is lead to a drain pumpingstation, so as to be discharged into a river and the like where theinfluent is discharged and, with the underground drainage facility beingsuitable for reducing power consumption of drainage pumps, reducingvolume or capacity of a pump well or time lag or delay in thefollowing-up of flowing-down of the upstream influent at the start ofthe drainage pumps, and/or for measuring an upsurge at a suspension ofoperation of the pump. Recently, large underground drainage facilitieshave been proposed, wherein an inflow water channel having a largecross-sectional area is disposed at the deep location under the groundfor a long distance. Underground facilities having a large depth in asolid or strong ground of a deep layer do not effect or influence anupper structure, and generally a depth equal to or greater than 50 mfrom the surface level is provided. Conventionally, open channel flowoperation drainage systems, wherein water flows down at a water levelhaving a free surface in a conduit have been utilized, because inflowingwater channels are not too deep and have a small distance, as comparedwith large underground drainage facilities of the type describedhereinabove. However, closed channel flow operation wherein water flowsdown at a water level, in which the water fills the entire conduit havebeen proposed and the mixed flow operation of open channel and closedchannels has also been considered. Either of these proposals howeverhave a storage or reservoir tank for causing the same to have storagecapabilities. If drainage pumps are installed in the open channel flowoperation, pumps having a large capacity and pressure head are required,and the capacity of prime movers also increases. Furthermore, a valve onthe discharge or delivery side is also required which has a large borediameter and a high pressure, and a prime mover for opening and closingthe valve also increases in size. If a large underground drainagefacility is built in a conventional manner, in a relatively smallunderground drainage facility, not only do the constructional costsincrease, but also there is an increase in the operating expenses. Thus,the conventional, relatively small underground drainage facility isuneconomical.

Moreover, it is necessary to provide a storage tank and to increase thecapacity of the pump well because the storage advantages are reduced inthe mixed flow operation of open channel and closed channel. Thislikewise increases construction cost.

Further, since the inflow water channel is lengthened considerably,water on the upstream side cannot be moved immediately following anoperation of drainage pumps, even if the drainage pumps are run. In amethod in which drainage pumps are operated only in response to a levelin a conventional pump well, there is a problem of delay or time lag infollowing flowing-down, which leads to an overflow of rivers or the likeon the upstream side.

On the other hand, in the underground drainage facility, in order for adrainage of an estimated amount of water to be effected due to an abruptincrease in a quantity of inflow due to a rainfall, a so-called waitingrunning is required in which running of drainage pumps starts before theinfluent reaches the pump well, that is, from a condition where a waterlevel within the pump well is low. In a case of such waiting running, itis desired that a quantity of discharge of the drainage pumps isadjusted or regulated easily and economically in accordance with achange in a quantity of inflow. In order to satisfy such demand, in, forexample, a Japanese Patent Unexamined Publication No. 57-1286092,vertical-shaft adjustable vane pump is proposed in which a vane or bladeangle of a pump impeller is variable.

Conventionally, a vertical-shaft adjustable-vane pump is used as acirculating pump, which circulating pump has a relatively low pressurehead of, for example, equal to or less than about 30 m. However, aconventional vertical-shaft adjustable-vane pump is not used as adrainage pump which has a high pressure head such that the totalpressure head reaches 50 to 60 m and which has a large capacity, for thefollowing reasons.

When the total pressure head increases or becomes high, a fluid forceapplied to the adjustable vanes increases correspondingly. Accordingly,a load applied to a blade angle operating mechanism which regulates ablade or vane angle of the impeller increases, so that the vane-angleoperating mechanism increases in size. On the other hand, since there isa limitation in dimensioning, the blade-angle operating mechanism mustbe received in a limited space within a hub of the impeller, there isalso a limit in an allowable load of the vane-angle operating mechanism.Accordingly, an adjustable vane pump cannot be applied to a drainagepump which is high in total head and which is large in capacity, as itis.

When a total pressure head increases, a specific speed Ns expressed bythe following equation must be reduced to a value less than theconventional one. Accordingly, there is a problem that efficiency andsuction performance are reduced. Specifically, in the followingequation, the rotational speed N is determined by suction pressure ofthe pump and a cavitation condition, and a discharge O and a pressurehead H are given from the drainage plan. Accordingly, if the pressurehead H increases, the specific speed Ns must necessarily be reduced to alow value. ##EQU1##

However, generally an adjustable impeller vane is arranged such that ashaft thereof is rotatably supported by a hub supported by a driveshaft, and is rotated about the axis of the shaft to adjust the vaneangle. Accordingly, a tip surface on the side of a casing of theimpeller and a hub surface on the side of a drive shaft must be formedrespectively into concentric spherical surfaces to conform to an innersurface of the casing and an outer surface of the hub. In view of suchrestriction on shape there is a problem that, if the specific speed islow the efficiency and the suction performance are degraded.

SUMMARY OF THE INVENTION

It is an object of the invention to solve the above-discussed problemsof the prior art, and it is a first object of the invention to providean underground drainage facility and a method of running drainage pumps,in which it is possible to save running cost by reduction in power ofthe drainage pumps, and to reduce construction or building cost.

Another object of the invention is to provide an underground drainagefacility of high reliability, in which, even if follow-up delay or timelag of influent flow on the upstream side, upsurge at the time ofsuspension of drainage pumps, or the like occurs, rivers and the like onthe upstream side do not overflow.

Yet a further object of the invention is to provide an adjustable vanepump which is suitable for use in high pressure head and large capacity.

In accordance with the present invention, an underground drainagefacility includes a drainage pump constructed such that an inflow waterchannel is not an open channel, but an estimated quantity of water isdischarged after the inflow water channel has beer brought to a closedchannel, and discharge operation even in the case of open channel.

Further, the underground drainage facility is characterized in that anadjustable vane pump or a rotational speed control pump is used as adrainage pump, and delay in drainage is made possible.

Furthermore, the underground drainage facility is characterized in that,as another means, the drainage pump comprises pumps of small capacityand high pressure head and pumps of large capacity and low pressure headarranged respectively at locations where an estimated quantity of wateris discharged in the case of an open channel and a closed channel andthe pumps of high pressure head and small capacity run in drainagewaiting.

An underground drainage facility according to the invention ischaracterized in that a height of an overflow weir such as rivers,closed conduits, drainage channels or the like on the inflow side is sodetermined as to be lower than the maximum water level, thus causingwater to be introduced into the underground inflow water channel.

Furthermore, the underground drainage facility of the present inventionis characterized in that, the further upstream the pump, the larger thesize of, for example, a diameter of inflow vertical shaft with respectto a quantity of inflow.

According to the present invention an adjustable vane pump is providedwhich comprises a vertical-shaft multi-stage adjustable-vane pump inwhich a plurality of vertical-shaft pumps are connected to each other onthe same axis in a multi-stage manner, and the vertical-shaft pump of atleast one stage comprises adjustable impeller vanes so supported to makea vane angle variable with respect to a drive shaft, and a vane angleoperating mechanism for rotating the adjustable impeller vanes about asupport shaft to adjust the vane angle.

Since the construction of the drainage pump is determined so as to becapable of draining an estimated quantity of water in the case of aclosed channel, not in the case of an open channel, the total pressurehead of the pump is reduced, and the power for draining the samequantity of water is reduced. In this case, since operation with aclosed channel system is small in buffer advantage as compared with anopen channel, water can overflow if water level in the pump well risesquickly and the elapsed time until a start of the pump is increased.

Such situation can be met with by a pump with adjustable vanes, andoperating the pump may be constructed in such a manner that the pumpstarts at a fully closed position of the vane angle (the minimum vaneangle) when water within the pump well does not rise or the water startsto rise, and as water level of the pump well, the vane angle is openedto maintain the water level of the pump well constant.

Furthermore, the use of an adjustable vane pump makes it possible tobring the initial quantity of discharge water to a small quantity. If aweir is provided on the discharge side, a discharge valve can beeliminated.

Moreover, floodwater on the upstream side can be prevented by providinga start timing of the adjustable vane pump dependent upon not only awater level in the pump well, but also a water level in the inflowvertical shaft on the upstream side. The pump is operated with the vaneangle fully closed just before stoppage of the pump so that it ispossible to reduce an upsurge at stoppage.

This is also possible if a rotational-speed control pump is used. Itsuffices that the pump start at low speed rotation, and the rotationalspeed rise as water level within the pump well rises.

Moreover, in place of the use of an adjustable vane pump, it is alsopossible to install pumps which comprise pumps of a small capacity and ahigh pressure head and pumps of a large capacity and a low head. Thatis, this is made possible by running pumps of a small capacity and ahigh pressure head over a period of time from the delayed running atfully closed vane angle to drainage of a small quantity of water andrunning pumps of a large capacity and a low pressure head duringdrainage running after the rise in water level in the pump well. Ofcourse, it is also possible to increase the capacity and the pressurehead of the pumps in a three stages and four stages manner on the basisof the plan of an underground drainage facility. Next, if overflow weirsare provided on rivers, covered conduits or flood control channels onthe inflow side, and are lower in height than the maximum water levelsin rivers, covered conduits or floor control channels so as tocompensate for a quantity of water corresponding to upsurge at stop ofpump, it is possible to make water levels in rivers, covered conduits orflood control channels on the inflow side lower than the maximum waterlevel, even if the upsurge occurs at stopping of the pump.

Further, it can take several tens of minutes until water in the inflowwater channels immediately below each overflow weirs starts to moveafter running of the pump, in the case where the inflow water channelsextend over long distances. In order to cope with this, the heights ofthe weirs are lowered below the maximum water levels to compensate forquantities of water corresponding to the quantity of inflow during this,whereby it is possible that water within the inflow water channelsstarts to move while water levels therein are lower than the maximumwater levels.

Furthermore, this is made possible by relatively enlarging inflowvertical shafts in relation to quantities of inflow as it goes towardthe upstream side since follow-up characteristics of water become moredegraded as it goes toward the upstream side.

On the other hand, since the adjustable vane pump according to theinvention is a vertical-shaft multi-stage adjustable-vane pump whichcomprises a plurality of vertical-shaft pump stages connected to eachother on the same axis in a multi-stage manner, and in which avertical-shaft impeller of at least one stage is composed of adjustableimpeller vanes, the pressure head born by the adjustable vane impellerstage is less than the total pressure head of the entire pump.Accordingly, it is possible to reduce a load applied to theadjustable-vane operating mechanism, so that the operating mechanism isreduced in size, and can be received within the impeller hub.Furthermore, since the specific speed is not required to be reduced, itis possible to maintain pump efficiency and suction performancefavorable. As a result, it is possible to realize an adjustable vanepump suited for the use involving a high head and a large capacity, thatis, suitable for a drainage pump for a-high-depth underground drainagefacility. Thus, it is possible to easily and economically adjust adischarge of the drainage pump to waiting running or a change in thequantity of inflow.

Moreover, if all of the stages are constituted by adjustable vane pumps,regulation of the discharge is further facilitated.

In the case where a plurality of stages are constituted by adjustablevane pumps, a vane-angle operating mechanism is preferably constructedsuch that a drive shaft of each adjustable vane pump is formed to behollow, an operating shaft is inserted into a hollow portion, theoperating shaft and adjustable impeller vanes are connected to eachother by a link mechanism, and an axial movement of the operating shaftis converted into a vane-angle rotational motion of the adjustable vanesby the like mechanism. With the arrangement, since the vane angle of theimpeller of each stage can be regulated in interlocking manner by asingle operating shaft, the arrangement can be simplified.

In the case where a part of the stages are constituted by adjustablevane impellers, it is preferable that pumps on the upper stage sideincludes adjustable vane impellers. If done the other way around, thesuction pressure of the fixed vane pump in the upper stage is reduced tothreaten cavitation when the vane angles of the impellers on the lowerstage side are fully or nearly closed.

For the similar reasons, in the case where adjustable vane pumpsconstitute two stages or more, the vane-angle operating mechanism ispreferably set such that vane angles on the lower stage side come toangular positions slightly larger than the minimum vane angle (closure)when vane angles on the upper stage side are brought to the minimum vaneangle (closure). Further, it is possible to improve PNSH performanceduring running at large flow rates as compared with the case where vaneangles of the upper and lower stages are set to the same values, whileit is possible to shift flow rates of each impeller at the start ofbackflow and at inflection points of a pressure head curve duringrunning of low or small flow rates. Thus, there can be provided pumps ofstable head curves.

Furthermore, an arrangement is preferable in which a casing, a driveshaft and a vane-angle operating shaft of a multi-stage vertical-shaftpump are made separate for the respective stages, and these parts of therespective stages are coupled to each other by connecting means such asa flange connection, screw coupling or the like. With the arrangement,disassembling for assembling, maintenance or the like can befacilitated.

Other objects, features and advantages of the invention will becomeapparent from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal schematic view of an underground drainagefacility according to an embodiment of the invention;

FIG. 2A is a schematic cross-sectional view of a pump well;

FIG. 2B is a graphical illustration of pump running conditions;

FIG. 3A is a diagrammatic illustration of a pump running condition;

FIG. 3B is a cross-sectional view of a pump well;

FIG. 4 is a diagram illustration of running conditions of the embodimentaccording to the invention, which uses adjustable vane pumps;

FIG. 5 is an enlarged schematic view of a pumping station, to which avertical-shaft multi-stage adjustable-vane pump according to theinvention is applied;

FIG. 6 is a cross-sectional view showing a vertical-shaft multi-stageadjustable-vane pump according to an embodiment of the invention;

FIG. 7 is a cross-sectional view of a vertical-shaft multi-stageadjustable-vane pump according to another embodiment of the invention;

FIG. 8 is a longitudinal schematic view of an underground drainagefacility according to another embodiment of the invention;

FIG. 9 is a diagrammatic illustration of a running condition of theembodiment according to the invention, in which a small-capacity andhigh pressure head pump and a large-capacity and low pressure head pumpare combined with each other;

FIG. 10 is a longitudinal schematic view of an underground drainagefacility according to another embodiment of the invention; and

FIG. 11 is a longitudinal cross-sectional view of an embodiment of theinvention in which an actuator of a vane-angle control unit in thevertical-shaft multi-stage adjustable-vane pump shown in FIG. 6 isreceived in an inner casing of an upper-stage adjustable-vane pump.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals are usedthroughout the various views to designate like parts and, moreparticularly, to FIG. 1, according to this figure, drainage flowing intosmall river, on the earth's surface, covered conduits, flood controlchannels or the like flows into an inflow water channel (a largeunderground water channel or an underground floodway) 4 through aplurality of vertical inflow shafts 1, 2 and 3 connected thereto. Thedrainage flowing into the inflow water channel 4 flows down into a pumpwell 6 at a pump station to be pumped by a pump 7, and is dischargedinto a large river, which is the place where influent is discharged,through a discharge pipe 10 and an overflow weir 11. Further, an airshaft 5 is suitably provided in the inflow water channel 4.

A characteristic and specification of the pump 7 is determined such thata predetermined estimated quantity of water can be discharged on thecondition that incoming water flows down through the inflow waterchannel 14 in a full state, that is, in closed channel operation.

When water flows from the vertical inflow shaft 1, 2 and 3 to fill theinflow water channel 4 to make the same a closed channel, a water levelin the pump well 6 rises, and an actual lift of the pump 7 is reducedand is made less than that when an estimated quantity of water isdischarged from a condition of an open channel. As shown in FIGS. 2A and2B, since a pump P₁ can discharge an estimated quantity of water withwater channel opened, H₁ is required for an actual head and power alsoincreases. On the contrary, since a pump P₂ can discharge an estimatedquantity of water with the water channel closed, H₂ is sufficient forthe actual head, and power also decreases.

A position where the pump 7 is installed is desirably determined suchthat in terms of a tendency in a characteristic curve Q-H of the pump,no-discharge operation is not effected even at the maximum actual head,as shown in FIGS. 3A and 3B, but a quantity of water more than anestimated quantity of water of 30-50% can flow. If the position wherethe pump is installed is determined such that the estimated quantity ofwater flows with the channel closed as described above, considerablereduction in power can be realized.

Subsequently, if the pump 7 illustrated in FIG. 1 includes by anadjustable vane pump, further advantages are realized. Since anadjustable vane pump requires less power when a vane angle is at aboutthe minimum value, continuous running is possible even in theno-discharge operation. Accordingly, waiting running is made possible.

Now, it is assumed that the pump starts at the minimum vane angle whenwater level in the inflow water channel 4 is L₁ in the opened conditionshown in FIGS. 3A and 3, and the vane angle is gradually opened when thewater level rises to reach a level L₂. Then, as running point shifts to1 to 2 to 3 to 4 to 5 in FIG. 4. As the quantity of inflow furtherincreases, the water level rises and the actual pressure head isreduced. Accordingly, the running point shifts from point 5 to point 6and discharge of the estimated quantity of water. Normally, vanes of themovable vane pump can be operated from a fully closed position to afully opened position within one to three minutes or so. Accordingly, ifthe pump is run in waiting with the channel opened, a size or dimensionof the pump well can be determined such that HWL is not reached untilthe vane angle is changed to a fully opened position. Thus, the pumpwell 6 having a small sized serves the purpose. Moreover, since the vaneangle is small at initial discharge of water and hence a quantity ofdischarge is small, it is unnecessary to provide a discharge valve in aconventional manner. Only provision of a weir on this side of the placewhere water is discharged on the discharge side makes it possible toprovide a system. It is possible to dispense with a discharge valve of alarge opening diameter for high pressures.

Further, as a method of starting the adjustable vane pump, it ispossible that not only a water level in the pump well, but also a waterlevel in the upstream inflow water channel and the upstream inflowvertical shaft are monitored, and the pump is started when the waterlevel rises. In some large underground drainage facilities, the pump 7is so different from the inflow vertical shafts that it takes severaltens of minutes until water in the neighborhood of the inflow verticalshafts moves after the starting of the pump. As a countermeasure forthis, it is possible to prevent flooding due to follow-up delay bystarting the pump to begin a discharge of water by a small quantity whenwater levels within the respective inflow vertical shafts start to rise.

Furthermore, upsurge can occur in an inflow water channel system when anormal fixed-vane water discharge pump is provided and if so, rivers,covered conduits, flood control channels and the like can overflow waterdue to upsurge at stop of the pump. With an adjustable vane pump,however, upsurge in the inflow water channel system can be considerablyreduced by stopping the adjustable vane pump after waiting running withthe vane angle nearly closed while the vane angle is gradually closed.The above-described advantage can also be achieved by employing, as thepump 7, a pump in which rotational speed is controlled. That is, thepump suffices to be started at a low rotational speed at a water levelL₁ in the inflow water channel 4 which is in a state of an open channel,and it suffices to increase rotational speed when a water level L₂ isreached.

Moreover, also it is possible at a stopping of the running of the pumpsto reduce up surge in the inflow water channel system by stopping thepump after waiting running at low speed.

As shown in FIGS. 5 and 6, as the pump 7 a vertical-shaft multi-stageadjustable-vane pump is utilized having two vertical-shaft mixed-flowstages, with adjustable vane impellers 7a and 7b being connected to eachother in a two stage manner. The lower-stage adjustable-vane impellers7a have a suction port which is in communication with the pump well 6through a suction tube 21 in the form of an elbow, and a discharge portwhich is directly connected to the upperstage adjustable-vane impellers7b. The adjustable vane impellers 7b have a discharge port which isconnected to a discharge tube 10 through a discharge elbow tube 22, saiddischarge tube 10 being opened to a large river where discharge iseffected. A drive shaft of the pump 7 extends out upwardly from aportion of the discharge elbow tube 22, and is connected to a drivemachine 23 through a coupling. As described hereinafter, the drive shaftis hollow, and an operating shaft for adjustment of a vane angle isinserted into the hollow portion of the drive shaft. A vane-anglecontrol unit 24 is connected to an upper end of the operating shaft.Here, an embodiment of a mixed-flow adjustable-vane will be described.However, the embodiment may be one of axial flow type.

As shown in FIG. 6, principal portions of the respective adjustable vanepumps 7a and 7b are identical to each other. An outer shell of theadjustable vane pump 7a is formed into a configuration of rotationsymmetry and comprises an outer casing 31 and a casing liner 32connected to the suction side of the outer casing 31. An inner casing 33of rotation symmetry is fixed within the outer casing 31 by guide vanes34 with its axis of rotation symmetry corresponding to that of the outercasing 31. A hollow drive shaft 35 is arranged inside the inner casing33, and is supported on the inner casing 33 by a bearing 36. An impellerhub 37 is mounted on a lower end of the drive shaft 35 in flangedmanner. The impeller hub 37 has its outer peripheral edge mountedslidably on an outer periphery of the lower end of the inner casing 33through water seals. A plurality of impellers 38 extending toward aninner surface of a casing linear 32 are mounted on the impeller hub 37.Each of the impellers 38 is mounted on the impeller hub 37 through astem shaft 41 which is supported by two bearings 39 and 40 such thatvane angles can be changed. Moreover, an impeller hub cover 42 having aconfiguration which forms an extension of the inner casing 33 is mountedon the suction side of the impeller hub 37. An operating shaft 43 isextended through a hollow portion of the drive shaft 35 and a throughbore centrally formed in the impeller hub 37. A spider 44 is mounted ona lower end of the operating shaft 43, and is connected to an arm 45mounted on the stem shaft 41, by a turnbuckle 46 through a ball joint.The arm 45, the turnbuckle 46 and the ball joint constitute a linkmechanism for converting vertical linear motion of the operating shaft43 into vane-angle rotational motion of the impeller 38. A conventionalmechanism of the type described, for example, in Japanese PatentUnexamined Publication No. 1-187399, may be employed as the linkmechanism.

The adjustable vane pump stage 7b, having a pair of casings 31 and 32 ofthe same construction as that in the pump stage 7a, is connected to anupper portion of the adjustable vane pump stage 7a formed in thismanner. An upper end of the drive shaft 35 of the adjustable vane pumpstage 7a is connected to an impeller hub 37 of the adjustable vane pumpstage 7b by a flange or the like. Further, the upper end of theoperating shaft 43 of the adjustable vane pump stage 7a is connected tothe lower end of an operating shaft 43' of the adjustable vane pumpstage 7b by a screw coupling 47. More specifically, the upper end of theoperating shaft 43 of the adjustable vane pump stage 7a and the lowerend of the operating shaft 43 of the adjustable vane pump stage 7b arethreaded to provide male threads which are to be screwed into thecoupling 47 formed with female threads. Upper ends of a drive shaft 35and the operating shaft 43 of the upper adjustable vane pump stage 7bare extended straight upwardly from the discharge elbow tube 22 as shownin FIG. 5, and are connected to the drive machine 23 and the vane-anglecontrol unit 24, respectively. The vane-angle control unit 24 isprovided with an actuator which advances and retracts the operatingshafts 43 axially. For this actuator, a hydraulic or pneumatic cylinder,an electric motor or the like is used.

A basic operation will first be described. When running of the drivemachine 23 starts, the upper-stage impeller 38 is rotated through theupper-stage drive shaft 35 and the impeller hub 37. Simultaneouslytherewith, the lower-stage impeller 38 is rotated through thelower-stage drive shaft 35 connected to the upperstage impeller hub 37and the lower-stage impeller hub 38. This inflow water within the pumpwell 6 is drawn or suctioned through the suction elbow tube 21 to bedischarged into a large river through the discharge tube 10. At thistime, since the adjustable vane pump stages 7a and 7b are connected inseries to each other, a full or total pressure head of the pump 7 is thesum of total the pressure heads of the respective pumps 7a and 7b. Inother words, the total pressure heads of the respective stages 7a and 7bmay be smaller than a required head determined by the drainage plan, andmay be about 1/2, for example. Accordingly, since a load applied to theimpellers 38 is reduced accordingly, it is possible to reduce a loadapplied to the vane-angle operating mechanism. As a result,constitutional elements of the vane-angle operating mechanism can besimilar in size to the conventional ones, so that it is possible toincorporate the vane-angle operating mechanism into the impeller hubs37. Since the total pressure head per stage is small, it is possible tomaintain specific speed large. Accordingly, it is possible to realize anadjustable vane pump which avoids cavitation, is high pressure inefficiency, and is suitable for use of high head and large capacity, incontrast to an adjustable vane pump of single stage type.

When the operating shafts 43 are axially displaced by the vane-anglecontrol unit 24, the vane angle of the respective upper-stage andlower-stage impellers 38 can simultaneously be adjusted in opening andclosing directions through the spiders 44, the turn buckles 46 and thearms 45. By doing so, it is possible to vary the discharge of the pump 7within a wide range, and considerable regulation of the pump performanceis made possible. Accordingly, the pump is favorably applied to waitingrunning or to an underground drainage facility in which a quantity ofinflow water varies widely.

Furthermore, it is preferable in the vertical-shaft multi-stageadjustable-vane pump illustrated in FIG. 6 to set the axial positionalrelationship between the operating shafts 43 and the spiders so that thevane angle of the impeller 38 of the lower-stage adjustable-vane pump 7ais made slightly large (on the degree of 1-2 degrees, for example) thanthe vane angle of the impeller 38 of the upper-stage adjustable vanepump 7b. By doing so, the following advantages are realized.

Even if the vane-angle opening degree of the upper stage pump 7b becomesminimum to present a closed condition, the vane-angle opening degree ofthe lower-stage pump 7a is slightly open. Accordingly, it is possible tosecure a suction pressure of the upper-stage pump 7b of a predeterminedvalue or more. Thus, it is possible to positively prevent cavitation ofthe upper-stage pump 7b from occurring due to reduction in suctionpressure.

Since a large vane angle is generally favorable in anti-cavitationperformance in large flow rates the above arrangement is suitable for acase where the pump 7 is used at flow rates greater than a designedpoint. In this connection, although the upper-stage pump 7b becomesunfavorable in anti-cavitation performance at high flow rates, thesuction pressure in the upper stage is got up by the lower stage.Accordingly, in the present embodiment, cavitation does not become aproblem.

If the vane angle is changed flow rates at which stall or counterflow offluid inherent in flow of small flow rate is generated change. However,a difference provided between the upper-stage and lower-stage vaneangles can prevent stall and counterflow from being simultaneouslygenerated both in the upper and lower pumps 7a and 7b, so that it ispossible to effect steady running even at small flow rates.

Further, the vertical-shaft multi-stage adjustable-vane pump illustratedin FIG. 6 is constructed such that the casings, the drive shafts, theoperating shafts and the like are distinct and are provided for therespective stages, and are connected to each other by couplings such asa flange or the like to make assembling and disassembling of the pumpeasy. More specifically, in assembling the pump, the upper-stageadjustable-vane pump stage 7b is first assembled except for the casingliner 32. The lower-stage operating shaft 43 is next connected to theupper-stage operating shaft 43 by the screw coupling 47 and,subsequently, the lower-stage drive shaft 35 is joined to theupper-stage impeller hub 37. Next, after the mounting of the upper-stagecasing liner 32, the adjustable-vane mixed flow ball section of thelower adjustable-vane pump stage 7a is assembled. In disassembling thepump, the upper-stage adjustable-vane mixed flow portion is disassembledafter the adjustable-vane mixed flow ball section, the drive shaft 35and the operating shaft 43 of the lower adjustable-vane pump stage 7aare dismounted in the reverse order.

In the embodiment of FIG. 7, a vertical-shaft pump 7c of a fixed vanetype replaces the lower adjustable-vane pump stage of the embodimentillustrated in FIG. 6. The upper adjustable-vane pump stage 7b is of thesame construction as that of the embodiment illustrated in FIG. 6. Thelower fixed vane pump stage 7c is constructed such that an impeller 50with the vane angle fixed is mounted on an impeller hub 49 providedrotatably with respect to the inner casing 33.

According to the present embodiment, the adjustable-vane pump stage 7bis connected in series to the fixed vane pump stage 7c and so the totalpressure head of the pump 7 amounts to the sum of the total pressureheads of the respective pump stage 7b and 7c. Accordingly, theembodiment of FIG. 7 can be applied to a pump of high total pressurehead, as compared with an adjustable vane pump of a single stage.Furthermore, according to the embodiment of FIG. 7, the structure of thepimp becomes simple as compared with the embodiment illustrated in FIG.6, and a force required for adjusting the vane angle can also bereduced. On the other hand, pump performance due to regulation of thevane angle is subjected to a small change. In this connection, thearrangement of the upper and lower stage of the embodiment illustratedin FIG. 7 may be varied such that the upper stage becomes of a fixedvane type. In this case, a problem of cavitation arises in the upperstage when the lower-stage adjustable-vane pump is run in the vicinityof closure.

The embodiments illustrated in FIGS. 6 and 7 are illustrated as beingapplied to a vertical-shaft mixed flow pump and may be applied to avertical-shaft axial flow pump. Moreover, also the number of stages ofadjustable vane pumps connected in series to each other is not limitedto two stages and is appropriately selected in accordance with theestimated head.

FIG. 8 shows an embodiment in which the pump 7 of the embodimentillustrated in FIG. 1 includes a small-capacity and high pressure headpump 8 and a large-capacity and low pressure head pump 9 in place of theabove-described adjustable vane pumps. To obtain similar effects,running in the embodiment comprising the adjustable vane pumps in thevicinity of the full closure of the vane angles is run by thesmall-capacity and high pressure head pump, while running in thevicinity of the full opening of the vane angles is run by thelarge-capacity and low pressure head pump. Running characteristic of thepumps are shown in FIG. 9. Here, two kinds of pumps are shown. Ofcourse, it is needless to say that several kinds of pumps may beinstalled for several stages.

Effects of the above embodiments on upsurge at stoppage of the pumps andtime lag caused during a period of tine elapsed from the running of thepump until water in the inflow water channel starts to be moved will bedescribed hereinbelow.

Drainage from a river overflows a weir to flow into an inflow verticalshaft 1. At this time, a height of the weir is set such that the maximumwater level of the river is not reached even if a quantity of water dueto upsurge at stoppage of the pumps or a quantity of inflow compensatingfor a period of time elapsed until water in the inflow water channelimmediately below the overflow weir after pump running starts to flowenters the river. In this manner, there is removed a risk of floodwaterand the like even though there is follow-up delay of water due toupsurge at the time of stoppage of the pumps and the inflow waterchannel being long. Moreover, a small buffer of the entire undergrounddrainage facility serves the purpose.

FIG. 10 shows another embodiment for preventing floodwater due to thefollow-up delay of water in the inflow water channel from occurring. Inthe embodiment of FIG. 10, there is provided a buffer effect byrelatively enlarging inflow vertical shafts relative to quantities ofinflow as it goes further upstream in the light of the fact that thefurther it goes upstream the worse the follow-up of water in associationwith the pump 7.

As described above, the embodiments of the underground drainage facilityaccording to the invention can produce the following advantages.

Since the pump is installed at a location where an estimated quantity ofwater can be discharged in a closed channel, it is possible to reduce arequired power.

Since the pump waits for drainage, a small buffer of the undergrounddrainage facility such as a pump well or the like serves the purpose.

Since drainage of a small quantity of water is possible at starting ofthe pump, a discharge valve can be dispensed with.

Since the follow-up delay of the inflow water channel at starting of thepump and upsurge at stop of the pump can be reduced, a problem such asfloodwater or the like is eliminated.

Since inflow enters into the vertical shaft in an overflow manner,rivers, covered conduits and flood control channels can be utilized asbuffer, and it is possible to solve floodwater problems and reduce thebuffer of the underground drainage facility.

The further it goes upstream the greater a buffer effect becomesrelatively, so, there is eliminated problems such as floodwater and thelike.

FIG. 11 shows an embodiment in which the actuator of the vane-anglecontrol unit in the vertical-shaft multi-stage adjustable-vane pumpillustrated in FIG. 6 is received in an inner casing 33 of anupper-stage adjustable-vane pump 7b. As shown in FIG. 11, a hydrauliccylinder 55 is provided on an upper portion of an impeller hub 37 of theupper stage adjustable-vane pump 7b to be connected to a drive shaft 35.Operating shafts 57 and 58 are attached to a piston 56 of the hydrauliccylinder 55, and mount thereon spiders 44 fixedly. The operating shaft58 has a lower end thereof rotatably supported by an impeller hub cover60 which, in turn, is supported on a suction tube 21 by a support piece61. A hydraulic or oil passage in communication with a hydraulic chamberin the cylinder 55 is formed through the operating shafts 57 and 58. Thehydraulic passage is in communication with a hydraulic source throughhoses 62 which are extended to the outside out of the impeller cover 60.Further, boss oil or boss hydraulic fluid is supplied to a bearingsection for the operating shaft 58 of the impeller hub cover 60 througha hose 63. With the arrangement, hydraulic oil is supplied to anddischarged from the hydraulic chamber of the hydraulic cylinder 55through the hoses 62, to drivingly displace the operating shaft in anaxial direction to thereby control the vane angles. According to thepresent embodiment, it is possible to compact the vane-angle controlmechanism. In this connection, the vane-angle control mechanismaccording to the embodiment of FIG. 11 may, for example, be a mechanismof the type described in, for example, Japanese Patent UnexaminedPublication No. 58-35294.

In the underground drainage facility of the present invention, it ispossible to save power for driving the drainage pump, and the size ofpump station can be reduced, so that cost for the building orconstruction and running cost can be reduced.

Moreover, there can be provided a highly reliable underground drainagefacility which will not cause rivers on the upstream side and the liketo overflow in spite of the follow-up delay of the inflow water on theupstream side and upsurge at stoppage of the pump.

Furthermore, with the construction of the vertical-shaft multi-stageadjustable-vane pump of the present invention, it is possible torestrain the total pressure head per stage of the adjustable vane pumpso that the vertical-shaft multi-stage adjustable-vane pump can beapplied to the use of high pressure head and large capacity. As aresult, there can be provided a pump suitable for an undergrounddrainage facility which involve running and fluctuation in the quantityof inflow.

What is claimed is:
 1. A vertical-shaft multi-stage adjustable-vane pumpcomprising a plurality of vertical-shaft pump stages connected to eachother on the same axis in a multi-stage manner; at least two of saidpump stages having a vertical-shaft impeller in the form of anadjustable vane impeller supported such that a vane angle is variablewith respect to a drive shaft, and a vane-angle operating mechanism forrotating said adjustable vane impeller about a support shaft to changethe vane angle, wherein said vane-angle operating mechanism sets thevane angle of the lower stage of said at least two stages to be slightlygreater than a minimum vane angle when the vane angle of the upper stageof said at least two stages is at the minimum vane angle.
 2. Avertical-shaft multi-stage adjustable vane pump as claimed in claim 1,wherein a first one of said vertical-shaft pump stages has a suctionport and a discharge port, and a second one of said vertical-shaft pumpstages has a suction port and a discharge port, said vertical-shaftmulti-stage adjustable vane pump further comprising means connecting thedischarge port of said first one of said vertical-shaft pump stages tothe suction port of said second one of said vertical-shaft pump stagesto connect said first one of said stages and said second one of saidstages in series with a common fluid flow passage.